1. Field of the Invention
The present invention relates generally to a photographing lens interchangeable system autofocus single-lens reflex camera and, more particularly, to a back-focal distance control system autofocus single-lens reflex camera for performing autofocusing (AF) by adjusting a flange-focal distance.
2. Related Background Art
There exists a system of adjusting a focal point on a film plane by moving a film in the optical-axis direction of a photographing lens as a system of adjusting the focal point of the camera. There also exists a system of adjusting the focal point by regulating a range ring of the photographing lens.
A camera adopting the former film plane moving system was introduced in the Back-Focal Distance System (pp. 160 and 161, the issue of March, 1953, Shashin-Kogyo) of the Mamiya-Six (a camera brand name of Mamiya Camera, Co., Ltd.) In the camera taking this Back-Focal Distance System, as a matter of course, a shutter speed, an aperture (an adjustment of exposure) and also an adjustment of a focal length are manually performed.
FIG. 31 is a camera body cross-sectional view illustrating a mechanism in the vicinity of the film plane of this camera. A film chamber P accommodates a film. A member E receives the film plane. The film surface holding member E has rails provided up and down, and the film surface is received by this portion. A camera body includes two lengths of shafts S.sub.1, S.sub.2 extending vertically as illustrated in FIG. 31. The shafts S.sub.1, S.sub.2 are respectively fitted with cams by ones up and down, totally two pieces of disk-like cams C.sub.1, C.sub.2. A spring R is attached to upper and lower ends of the central portion of the film surface holding member E. Both ends of the spring R are pushed against peripheral surfaces of the cams C.sub.1, C.sub.2, resulting in a state where the cams C.sub.1, C.sub.2 are thrust in an arrowed direction D.
The shafts S.sub.1, S.sub.2 interlock with each other via an unillustrated gear. The cams C.sub.1, C.sub.2 rotate through the same angle with rotations of the shaft S.sub.1, S.sub.2. The film surface moves back and forth with rotations of these cams C.sub.1, C.sub.2.
An unillustrated gear is fixed to the uppermost portion of the shaft S.sub.1. This gear is partly exposed outside from a rear surface of an upper cover of the camera. Accordingly, the photographer is capable of adjusting the focal point by manipulating the exposed portion of the gear with the thumb of a right hand while holding the camera. A range finder is interlocked to operate with rotations of the above gear. The focus adjustment can be confirmed through the range finder.
The above-described camera is of a manual focus adjustment system, wherein a back-focal distance is manually adjusted. This is a focus adjustment mechanism which is not adapted to a real situation when considering an actualization of the autofocus single-lens reflex camera.
Next proposed is another example of adjusting a position of a focal plane, wherein a CCD imaging device of an electronic still camera is moved (Japanese Patent Laid-Open No. 2-24640).
This proposal aims at obviating a problem caused when using an interchangeable lens of a photographing interchangeable type electronic still camera but a different camera, e.g., a silver halide camera. More specifically, the mount of the electronic still camera including an autofocusing apparatus assumes the same configuration of the mount of the interchangeable lens mounting unit of the silver halide camera including the autofocusing apparatus. Even if possible of mounting the silver halide camera interchangeable lens into the electronic still camera and driving the range ring of the photographing lens, though the photographing lens is stop-controlled to be focalized when installed in the silver halide camera, it happens that the photographing lens can be stopped so that the CCD imaging device enters the focal depth when installed in the electronic still camera, resulting in a defocus state. The arrangement for obviating this drawback is that the position of the CCD imaging device can be slightly shifted back and forth.
FIG. 32 is a cross-sectional view of the camera body, showing one example of the above electronic still camera. Referring to FIG. 32, a CCD 301 is employed as a solid-state imaging device. The numeral 302 represents a holding member of the CCD 301, and 303 designates a fixed unit of a camera body G. A piezoelectric element 304 serves to move the CCD imaging device 301 in the optical-axis direction. A focus-detection unit 305 measures a deviation of an image plane from the time when focalized on an arbitrary subject. This unit 305 is connected to a camera control circuit 319. The numeral 306 denotes a amount on the side of the camera body G. A camera-side electric signal contact 307 is held by the mount on the side of the camera body G. A return mirror 308 guides beams of light penetrating an optical system of an interchangeable lens unit H to a finder. An AF mirror 309 guides the beams passing through a half-mirror element of the return mirror 308 to the focus-detection unit 305. The numeral 310 represents a shutter, 313 designates a focusing lens, 316 indicates an AF motor, and 314 denotes a movable lens barrel for holding the focusing lens. A lens control circuit 318 includes a ROM for storing items of data such as an open F-number of the interchangeable lens, an image plane moving quantity with respect to the focusing lens 313, a focal length, a maximum defocus quantity and interchangeable lens identifying codes. Each time a power switch of the camera body is turned ON, or each time the interchangeable lens is replaced, the above data are transferred in the form of electric signals to the camera body.
When fitting the interchangeable lens unit H to the camera body G, this item of data is transferred as an electric signal to the camera body G. Then, the beams traveling through the interchangeable lens unit H are guided via the return mirror 308 to the finder. At the same time a part of the beams are incident on the focus-detection unit 305 through the AF mirror 309. The focus-detection unit 305 calculates a deviation quantity of the image plane and transfers this quantity to the camera control circuit 319. The camera control circuit 319 further converts a moving quantity of the focusing lens 313 and transfers this quantity to the lens control circuit 318 via the electric signal contacts 307, 312. The lens control circuit 318 converts data about the moving quantity given from the camera control circuit 319 into a rotational quantity of the AF motor 316. The AF motor 316 is thereby driven to move the movable lens barrel 314 in the optical-axis direction through a helicoid member 314a. Whether focalized or not is confirmed based on the data of the focus-detection unit 305 in this state. If not focalized, focusing is performed by repeating the above operations.
By the way, when installing an interchangeable lens of a different camera, though the lens can be moved to the vicinity of the in-focus position, a minimum quantity with which the movement of the focusing lens is controllable is too large for the camera body G at this time. The in-focus state can not be obtained in some cases. Under such circumstances, the arrangement in this example goes as follows. A status as close to the in-focus state as possible is attained with the focusing lens 313, and the image plane deviation quantity is measured by the focus-detection unit 305. Alternatively, if the image plane deviation quantity falls within a fixed value, a remaining image plane deviation quantity till entering an in-focus area is transferred to the camera control circuit 319. A voltage is applied to the piezoelectric element 304, and the CCD imaging device is moved by the image plane deviation quantity in the optical-axis direction, thereby focusing on the subject.
The focus adjustment of the above electronic still camera is based on a system of focalizing by rotating the range ring of the lens. When using the interchangeable lens of the different camera, and if not focalized only by the range ring of the lens, the CCD imaging device is slightly moved in the optical-axis direction to be set as close to the vicinity of the in-focus position. Essentially, focusing is performed by propelling the lens. The film plane mechanism is a mechanism for compensating a defocus if not focused.
On the other hand, in the latter system of focusing by adjusting the range ring of the photographing lens, the utilized versions are a system of incorporating the motor as a drive source into the body and a system of incorporating it into the lens.
When adopting any of the above systems (of incorporating the motor into the body or the lens), the AF single-lens reflex camera generally employs a manual focus lens and an adaptor to make usable lenses other than the AF interchangeable lens for an exclusive use. Thus, other autofocus lenses can be installed. In the lenses other than the AF interchangeable lens for the exclusive use, the focal point has to be adjusted manually.
From the background described above, the inventors of this application have developed a back-focal distance control system autofocus single-lens reflex camera capable of automatically performing the focusing operation by using, as a matter of course, the AF interchangeable lens for the exclusive use and even a conventional manual interchangeable system lens or other AF interchangeable lenses.
It is a first object of the present invention to provide a back-focal distance control system autofocus single-lens reflex camera capable of improving a cost performance by making it possible to use any types of interchangeable lenses including a manual interchangeable lens, an AF interchangeable lens for an exclusive use and other drive system autofocus interchangeable lenses as autofocus lenses.
Next, when considering the usability in the back-focal distance control system autofocus single-lens reflex camera possible of autofocusing as well as in the conventional manual interchangeable lens as stated above, it is required that a flange-focal distance be in a predetermined position in the manual focus operation. It is because the lens installed is employed according to its performance and because there is caused no deviation in the distance indication of the lens range ring. Accordingly, when changed over to manual control from AF control, it is desirable that the flange-focal distance be in the above-mentioned position.
Further, when switching OFF the power supply or unused for a long period of time, the flange-focal distance is thereafter required to be in the predetermined position in consideration of the portability or the case of the manual focus operation effected immediately after switching ON the power supply.
The conventional autofocus single-lens reflex camera is structured so that lens data can be transferred from the ROM incorporated into the lens to the body side by installing an AF only lens. In this specification "AF only lens" hereinafter means an AF lens for the camera of this invention. The ROM data defined as the lens data for so-called lens driving contain a focal length, an extension quantity of the lens and correction value of its position, etc.. Accordingly, there is exhibited such a characteristic that the AF operation is conducted accurately and quickly.
By the way, when performing autofocusing through not the AF only lens but other autofocus lens or the manual focus lens in the above autofocus single-lens reflex camera, some of the former lenses (not the AF only lens but other AF lenses) do not include the ROM for storing the lens data. The latter lens (the manual focus lens) has not transferring element such as the electric contact or the like for transferring the data to the body side, and, therefore, it is impossible on the body side to judge what kind of photographing lens to install. For this reason, it follows that the judgement is made based on only the AF data relative to the beams of light from the subject which have passed through the photographing lens, and the AF operation carried out. Consequently, there arises a problem, wherein a focusing speed is slower than in effecting autofocusing by obtaining the lens data.
It is a second object of the present invention to provide a back-focal distance control system autofocus single-lens reflex camera capable of exhibiting a good portability and accommodation when not in use without causing an deviation of scales of a range ring when manipulating the manual focus lens.
It is a third object of the present invention to provide a back-focal distance control system autofocus single-lens reflex camera capable of quickly focusing at a high accuracy with respect to all the lens installed.
Next, in a lens drive system autofocus single-lens reflex camera, it is obvious that a variety of interchangeable lens have a limit in terms of close-up photography. Even when canceling AF and manually adjusting the focal point, it is similarly impossible to carry out the close-up photography in excess of the limit. Under such circumstances, a method of installing a close-up ring between the lens and the lens mount is taken for the close-up photography exceeding the lens adjustment limit. In this method, however, it takes a good deal of labors to attach and detach the lens and the close-up ring, and the close-up ring has to be carried for the close-up photography.
It is a fourth object of the present invention to provide a close-up photographing mechanism of the back-focal distance control system autofocus single-lens reflex camera, by which macro photography much closer up to a subject than a close-up limit of the conventional lens can be attained.
Next, in the prior art autofocus single-lens reflex camera, as explained earlier, there exist the systems of driving the range ring by incorporating the motor into the body and into the lens as the system of driving the lens range ring for focusing. In any systems, when canceling AF and changed over to the manual mode, there is provided a clutch mechanism for enabling the manual mode by cutting off the lens drive system. Further, an AF/MF changeover switch is installed in a location restricted by the lens driving system. For this reason, the following drawbacks are produced. If the subject proves awkward with an AF focus-detection, or if the photographer desires for a switchover to the manual focus mode during the AF operation, it is impossible to simply quickly effect the switchover to the MF mode. The photography can not shift from the autofocus mode to the manual focus mode depending on the circumstances corresponding to situations of the subjects.
It is a fifth object of the present invention to provide an AF canceling device of the autofocus single-lens reflex camera, which enables the photographer to employ high-level photographic techniques by performing a quick and smooth shift from the AF mode to the MF mode during the AF operation.
It is a sixth object of the present invention to provide an autofocus single-lens reflex camera including two AF drive mechanisms and capable of quickly performing the AF operation by use of lens ROM data through an AF only lens by selecting the AF drive mechanism in accordance with a type of a photographing lens installed and also effecting the AF operation through even a conventional manual lens.
Next, as stated above, in the back-focal distance control system autofocus single-lens reflex camera constructed of a camera body fixed block, a movable block and a mechanism for connecting these blocks, a diaphragm interlocking pin of an ordinary lens has a limit in its length. Hence, there is a possibility in which the lens diaphragm interlocking pin comes off an auto diaphragm lever of a mirror box mechanism, depending on a relative moving quantity of the movable block with respect to the camera body fixed block.
It is a seventh object of the present invention to provide an auto diaphragm mechanism of an autofocus single-lens reflex camera, wherein the lens diaphragm interlocking pin can be surely driven with a high accuracy.
Moreover, in the back-focal distance control system single-lens reflex camera, the back-focal distance drive control inevitably involves a considerable weight and capacity, though it depends on a design configuration because of the movable block incorporating an aperture element, a focus-detection mechanism and a finder mechanism. An important subject is that the movable block is precisely driven at a high speed.
The conventional AF drive control takes such an arrangement that some allowance is given to the power of the drive motor, and the movement to an in-focus position is made while measuring a micro-unit moving quantity from an initial stage of driving. Accordingly, there is a defect, wherein if a distance from a present position to the in-focus point is large, it takes much time for in-focus driving.
It is an eighth object of the present invention to provide a drive mechanism of a back-focal distance control system autofocus single-lens reflex camera capable of precisely moving the movable block unit to the in-focus position at a high speed.